1. Field of the Invention
The present invention relates to a photo printer, and more specifically, to a photo printer with a vertically transmitted platen roller.
2. Description of the Prior Art
A thermal printing head (TPH) and a platen roller for carrying a print medium are two necessary parts in a dye-sublimation/thermal photo printer. These two parts are not contacting with each other when the photo printer is not printing but contacting and generating a contact force when the photo printer is printing. The contact force due to the mutual thrust of the TPH and the platen roller ensures that the inserted print medium is grabbed by the TPH and the platen roller and that the TPH can contact the print medium to sublimate dye onto the print medium.
The mechanism that draws the TPH and the platen roller close in a thermal photo printer in the prior art can be classified into two major classes. As disclosed in Japanese publication #P2003145819A, entitled “Thermal Transfer Printer”, the first class of mechanism introduces a platen roller frame that supports and brings the platen roller to approach the TPH curvilineally, while the second class of mechanism introduces a TPH frame that moves the TPH to approach the platen roller in a curvilinear manner.
It takes fewer elements for the first class of mechanism, which moves the platen roller by the platen roller frame to approach the TPH curvilineally, than for the second class mechanism. This means that the first class of mechanism is more suitable for applying to small thermal printers such as photo printers that produce 2-inch photos. However, in both the first class of mechanism and the second class of mechanism, the path of approach of the TPH and the platen roller is curvilinear, and therefore a space for a rocker arm, namely the platen roller frame or the TPH frame, is needed. The space must be for the rocker arm's exclusive use. In addition, since the platen roller frame or the TPH frame moves the platen roller or the TPH via a torque, significant rigidity of the frame material is required, and consequently it is nearly unavoidable to use a metal frame, which means higher cost of manufacture.